Atomic Layer Epitaxy of GaAs and InAs
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ATOMIC LAYER EP1TAXY OF GaAs AND InAs
WEON G. JEONG, E.P. MENU AND P.D. DAPKUS University of Southern California, Department of Materials Science, Electrical Engineering and the
Center for Photonic Technology, University Park, SSC-502, Los Angeles, CA 90089-0483 ABSTRACT The saturation behavior of growth of GaAs and InAs by atomic layer epitaxy is studied.
The growth rate is found to be strongly dependent on alkyl exposure time for the same total alkyl exposure per cycle. The longer the exposure time, the higher the saturated growth rate is. For short exposure, the growth rate saturates to a value less than one monolayer (ML)/cycle. Strong saturation of the growth rate to one ML/cycle is achieved for InAs at a growth temperature of 340"C with 3 sec of trimethylindium exposure. For GaAs, saturation of the growth rate to one ML/cycle is achieved at the growth temperature of 400"C with 10 sec of trimethylgallium exposure. At higher growth temperatures, the growth rate does not saturate but increases slowly with increasing exposure. The large physical size and finite decomposition time of the initial adsorbate are suggested as the cause for the dependence of ALE growth rate on alkyl exposure time. INTRODUCTION InlixGaxAs is used as a lattice matched heterojunction pair with InP or InA1As or as a strained quantum well with GaAs in various optoelectronic and high speed electronic devices. The growth of indium compounds by conventional metalorganic chemical vapor deposition (MOCVD) has been plagued by several problems that have frustrated attempts to obtain a consistent growth rate and abrupt heterojunctions [1]. Parasitic pre-reaction between indium source materials and hydrides, typically between triethylindium (TEIn) and PH3 or ASH3, makes the control of growth rate difficult. The use of trimethylindium (TMIn) instead of TEIn has alleviated the parasitic reaction but the transfer efficiency of TMIn by a carrier gas depends strongly on the surface area of the solid TMIn. Finally, intermixing of AsH3 and PH3 makes it difficult to obtain an abrupt compositional junction between arsenide and phosphide compounds [2]. Atomic layer epitaxy (ALE) is a relatively new epitaxial process, which is characterized by the separate exposure of reactants to the surface of the compound semiconductor substrate.
Owing to dependence on
saturated surface reactions, ALE has been demonstrated to have several advantageous properties in studies of II-V compound semiconductors [3,4] and GaAs ALE growth [5-8]. The crystal grows in a monolayer by monolayer fashion and very uniform layer thickness can be obtained over a wide area. Furthermore, the growth rate is relatively insensitive to the flux of reactants once they are supplied larger than a certain amount. Finally, the growth can be assisted by photo-excitation to achieve locally accelerated selective growth [9-12]. Separate exposure of the reactants also provides an opportunity to study and model the growth process in more detail [ 13-15]. From these Mat. Res. Soc. Symp. Proc. Vol. 145. ©
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